Pressure-treated wood

For years it's been the mainstay for making outdoor decks, swing sets, garden trellises and raised beds. Pressure-treated wood was first introduced in the 1960's. It revolutionized outdoor building projects by giving consumers a new treatment for wood that, like creosote, protected it from rot for 30 years. But, unlike creosote, it wasn't messy and seemed to be much safer.

The most commonly used pressure-treated wood is chromate copper arsenate, or CCA. This wood often has a "green" tinge to it, and it's widely available in lumber yards and home centers. But not for long. The EPA and the wood preservative industry have agreed this past winter to ban the sale and use of CCA-treated wood by the end of next year.

The concern is the arsenate, a chemical form of arsenic and a well-known poison. CCA-wood is pressure-treated with arsenate to kill any rot-causing organisms. The wood preservative industry claims that it is bound tightly to the wood through the preservation process and doesn't significantly leach into the soil. Independent studies claim otherwise. They show significant amounts of arsenate leach from new wood in particular. The concern is especially high for children playing on CCA-treated swing sets, where young kids may put their hands in their months after touching the swing sets, or eat the soil under the playground equipment. For gardeners it's even more of a concern, since edible plants such as grapes and vegetables may be grown on trellises or in raised beds made from CCA-treated wood.

The EPA is not calling for gardeners or consumers to replace old CCA-treated structures, since most of the arsenate seems to leach out of the wood within the first few years. However, for existing beds made from CCA-treated wood, I'd suggest digging out around the inside edge of the bed and lining it with four-millimeter thick plastic. This will create a barrier between the treated wood and the soil. Have the soil tested for arsenate, especially if you're growing edible crops. But since this wood is being removed from the market, what's a gardener to do if they want to build a new wooden raised bed? Well, there are some alternative materials to use when building a new bed.

Native woods such as cedar and hemlock, though expensive, are rot-resistant and can make for beautiful structures in the garden. And the wood-preservative industry is quickly coming up with treated wood alternatives such as ACQ, which features copper and ammonia as the protectants. More alternatives will become available soon. Plastic woods made from recycled products are also available and have a long life in the soil. Finally, consider other natural materials, such as rocks and bricks, to construct your beds. The look will be different, but it will serve the same purpose.

With a little thought and shopping, you can still create beautiful raised beds and arbors, but now with the peace of mind that they will be safe for everyone.

This is Charlie Nardozzi in Hinesburg.

Charlie Nardozzi is an all-around gardening expert with a special fondness for tomatoes and roses.